Field of the Invention
The present invention relates to an optical encoder.
Description of the Related Art
Optical encoders include one in which, as disclosed in Japanese Patent Laid-Open No. 2011-185806 and others, a mask having multiple slits (grating) is provided between a scale and a sensor (light-receiving element array). Using such a mask enables producing, in response to a relative movement of the scale and sensor, a sinusoidal signal with a far shorter signal period than an arrangement period of light-receiving elements in the light-receiving element array. Converting multiple sinusoidal signals whose phases are mutually different into position information by signal processing enables position detection with an extremely high resolution.
However, in such an optical encoder, change of a distance between the scale and sensor due to assembly errors such as mounting position variations of the scale, sensor and mask fluctuates a period of a spatial image formed on the light-receiving element array. This fluctuation decreases an amplitude of a position detection signal or changes a phase relation between the multiple sinusoidal signals, which may deteriorate position detection accuracy.